In recent years, detection information of various sensors, operation information of switches and the like have been transmitted via radio communication and it has been proposed to use an ultra wide band (hereinafter, abbreviated as “UWB”) communication system for this radio communication. In this UWB communication system, frequencies used are in a GHz band (e.g. 3.1 to 10.6 GHz) and a bandwidth is specified to be 25% or higher than a center frequency of communication or 450 MHz or higher. In the UWB communication system, upon transmitting data, ultra wide band communication is carried out using a pulse train composed of pulse signals synchronized with predetermined cycle timings. As one mode, without using a carrier wave, communication is carried out using a pulse train composed of pulse signals whose pulse widths are very short, such as 1 nsec or shorter (short pulse waves, ultra short pulse waves).
In this mode, one of differences between the UWB communication system and other communication systems is the presence or absence of the carrier wave. In other communication systems, a sine wave having a predetermined frequency is, for example, used as a carrier wave and communication is carried out by modulating this carrier wave in various manners. On the other hand, in the UWB communication system, communication is carried out by using short pulse waves in an ultra wide band without using a carrier wave (see, for example, patent literature 1). In the case of using OOK (On Off keying) in its modulation system, the value of a data is expressed by the presence or absence of a pulse similar to ASK (Amplitude Shift Keying) and non-coherent communication using no phase information in the value of the data becomes possible.
A reception device using the UWB communication system for transmitting data in a non-coherent manner using short pulse waves transmitted from a transmission device at regular time intervals includes an expander at an input stage for outputting an intermediate signal obtained by frequency-converting a reception signal. This expander includes an oscillator for outputting a station-transmitted signal having a frequency different from a center frequency of the reception signal and a waveform independent of the phase and waveform of the short pulse waves included in the reception signal, and a mixer for outputting the intermediate signal by multiplying the reception signal and the station-transmitted signal. The oscillator of the expander constructed as above constantly operates, causing large power consummation of the reception device.